My Apologies, Yes I did Sound Stupid
May 19, 2009
Okay Dr. Bob,
Student of Sociology here again and I hope you forgive me for my previous inane and stupid post. So here I ask again about why two hiv positive persons having to use condoms because of different subtypes and strains, will then the same HIV antibody test pick up both of their subtypes and strains since they are differnet enough to warrant protection from reinfection? I am resubmitting this question hoping this time you will answer. Thank you and I will learn more proper etiquette. I don't want to be a brat anymore. I want to help people. Thank you. Yes, I need zoloft.
Response from Dr. Frascino
Welcome back. Apology accepted.
Your confusion stems from an incomplete understanding of HIV types and subtypes as well as incomplete knowledge concerning how HIV-antibody tests are performed and what exactly HIV-antibody tests are designed to detect.
Briefly HIV-antibody tests (ELISA, EIA, rapid tests, Western Blots) are designed to determine if someone is infected with HIV-1 or HIV-2, irrespective of subtypes. There are two HIV types: HIV-1 and HIV-2, which show 40% to 60% amino acid homology (overlap). HIV-1 accounts for the vast majority of HIV infections worldwide. The small minority of HIV-2 cases originate from West Africa where the virus is endemic. HIV-1 is divided into subtypes designated A to K (collectively referred to as "M" subtypes) and O (for "other"). There are now also circulating recombinant forms (CRF). The major ones are CRF01_AE (a mosaic with sequences form clades A and E) and CRF02_AG. Subtype O shows 55% to 70% homology with the M subtypes. A new group of viruses labeled "N" for "new" has also more recently evolved. Over 98% of HIV-1 infections in the U.S. are caused by subtype B. Most non-B subtypes in the U.S. were acquired in other countries. The rare O and N subtypes are found primarily in West Africa.
The standard serological test for HIV consists of a screening ELISA followed by a confirmatory Western Blot, if the former is positive. Details of these two assays can be found below in a previous post.
The basic concept is that HIV-screening tests detect the presence of antibodies directed against a variety of core and envelope proteins found in all the common strains and subtypes. The only exception being certain O and N subtypes, which may be missed by these standard assays. However, as noted above, cases of O and N are extremely rare outside of West Africa.
I realize this response is a bit complex. I wanted to give you enough detail to reassure you that there is no credence to your hypothesis that HIV-antibody test sensitivity has anything to do with the risk of superinfection/dual infection for two HIV-positives having unsafe sex!
Technical Testing Question (what I meant to ask!) Apr 9, 2009
Dear Dr Bob,
My question is two fold, but has to deal with the fact that most ELISAs, including rapid tests, detect only gp41 antibodies:
I have seen people (confirmed positive with VL) with reactive ELISAs, but negative gp41 (& also 120) bands on their Western Blots. How is this so if they don't have gp41 antibodies?
Secondly, on the flip side, is it possible for someone not to develop these antibodies (as demonstrated by those WBs) and test negative on ELISA, but have the other bands present? Basically - can they present a false negative?
Thanks for your input, Dr Bob!
Response from Dr. Frascino
These types of basic technical questions are not the real purpose of this forum, so I'll be brief.
Your confusion has to do with the basic difference between the way a screening ELISA (EIA and rapid test) is actually performed compared with a confirmatory Western Blot test. These are two different types of test assays.
ELISA uses a mix of HIV antigens (proteins) produced in high titer in tissue culture systems or through recombinant molecular technology. These high-titer cell cultures are then lysed and the mix of soluble antigens is then coated onto the wells of a microtiter plate. The patient's serum is then added and if specific anti-HIV antibodies (many different types) are present they will bind tightly and specifically with the HIV antigens on the plate. After washing away the unbound material a goat antihuman antibody that binds to anti-HIV human antibody (which is bound to the HIV antigens on the plate) is added. The goat antihuman antibody is conjugated to an enzyme that cleaves a colorless substrate into a product that has color (usually yellow). The amount of color present is proportional to the amount of bound antibody and antigen. The amount of HIV can be determined semi-quantitatively by spectrophotometry. Basically this type of testing uses a variety of HIV antigens all mixed together.
The Western Blot test is also designed to detect the presence of anti-HIV antibodies. However, in addition to identifying the presence of such antibodies, it also allows determination of the specific antigen against which the antibodies are directed, including core (p12, p24, p55), polymerase (p31, p51, p66) and envelope (gp41, gp120, gp160).
Consequently the ELISA is the more "sensitive" test but the Western Blot is the more "specific" assay.
See, I told you this type of technical question is beyond the scope of this forum! Now can we get back to the questions concerning barely legal Russian hookers with the web feet?
Dr. Bob Please You Are An HIV Specialist May 18, 2009
Please help explain this to me, I can't even ask my primary care doc because he is not specialized in HIV. You however are. I will try to explain plainly and make sense of my question. Since it is that if two HIV positive people with different strains, subtypes, still have to have protected sex with eachother because of reinfection because they have different strains (subtypes), how is it then just one HIV antibody test is all that is needed to determine if a person is truly positive or negative after the window period of 3 to 6 months? These different subtypes and strains would be so different as to having different antibodies wouldn't they? Not to be a brat, but watch, even you won't answer this question and ignore it because it's scary and disturbing this truth and induces panic. Thanks in advance anyway. Student of Sociology
Response from Dr. Frascino
Why would you ask me to "please help explain" something to you and then say something as stupid as "watch even you won't answer this question and ignore it because it's scary and disturbing this truth and induces panic." Aside from the bad grammar, do you really think a statement like that would encourage me to respond? Your question is neither scary nor disturbing. It has a very simple, logical and scientific answer. I'll be more than happy to explain it to you if and when and if you resubmit your legitimate question without the inane postscript! This is an HIV/AIDS information Web site that provides science-based responses to questions. Truth does not induce panic. It provides enlightenment and understanding. "Student of Sociology," you have much to learn about sociology, not to mention appropriate etiquette and common sense when requesting a free service!
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